Abstract

Extensible Markup Language (XML), which provides a flexible way to define semistructured data, is a de facto standard for information exchange in the World Wide Web. XML employs a tree-structured data model. Therefore, an XML query typically consists of two parts: structure constraints and a value predicate. Furthermore, an XML query may be either a simple single-path query with or without a predicate, or a complex twig (branching) query with or without a predicate. Indexing plays a key role in improving the execution of a query. In this chapter we give a brief history of the creation and the development of the XML data model. Then we discuss the three main categories of indexes proposed in the literature to handle the XML semistructured data model. Finally, we discuss limitations and open problems related to the major existing indexing schemes.

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